Miaoyong Zhu

Oxidation induration process and kinetics of Hongge vanadium titanium-bearing magnetite pellets

The induration process and oxidation kinetics of Hongge vanadium titanium-bearing magnetite (HVTM) pellets have been investigated by employing X-ray diffraction, scanning electron microscope, energy-dispersive spectroscopy, thermogravimetric and differential thermal analysis and thermogravimetric and differential scanning calorimetry. The results indicated that HVTM was a high-chromium vanadium-bearing titanomagnetite containing 1.48 wt-% Cr2O3, and the crystal stock strength was 625 N. The compressive strength of HVTM pellets could be improved by increasing the roasting temperature and roasting time. Under the optimum conditions of oxidation roasting at 1200°C for 15 min, the compressive strength was found to be 2893 N. The phase transformations of the valuable elements could be described as follows: Fe3O4→Fe2O3; Fe2VO4→(Cr0.15V0.85)2O3; Fe2.75Ti0.25O4→FeTiO3→Fe9TiO15; FeCr2O4→(Fe0.6Cr0.4)2O4, Fe0.7Cr1.3O3, (Cr0.15V0.85)2O3. Three stages were identified during the induration process: initial oxidation, later oxidation, and haematite re-crystallisation, poly-crystallisation and induration. The development of strength mainly occurred in the last stage. Kinetic parameters of the oxidation process were determined from heating experiments. The results showed that the average value of activation energy was calculated to be 69.33 kJ mol−1 by the Flynn–Wall–Ozawa methods. This study aims to provide theoretical and technical bases for the effective utilisation of HVTM ore for use in either blast furnaces or shaft furnaces.

Characteristics of solute segregation in continuous casting bloom with dynamic soft reduction and determination of soft reduction zone

Abstract A mathematical model accounting for the discharge of solute enriched liquid from the mushy zone with soft reduction by one pair of pinch rolls was established, and the ratio of solute concentration in the mushy zone before and after soft reduction, named as solute segregation ratio, is proposed to describe the characteristics of solute segregation. The theoretical analysis of solute segregation ratio at different soft reduction positions shows that the start point of the soft reduction zone should not be greater than the minimum optimum soft reduction position and the end point of the soft reduction zone should not be less than the maximum optimum soft reduction position corresponding to minimum solute segregation ratio. The soft reduction industrial practices of steel YQ450NQR1 and steel 37Mn2 were carried out with the soft reduction parameters determined by the model, and results showed that the inner quality was improved.

Theoretical model for determining optimum soft reduction zone of continuous casting steel

Abstract A theoretical model for determining the optimum soft reduction zone of continuous casting steel was developed. According to the theoretical analysis of the solute segregation behaviour in the mushy zone with the soft reduction by one pair of pinch rolls, there is an optimum soft reduction position for each element of steel, and all optimum soft reduction positions of different solute elements should be included in order to eliminate the centreline segregation effectively. The theoretical analysis shows that the carbon content has a great effect on the optimum soft reduction zone, and the cooling rate could affect both the optimum soft reduction positions of the segregation prone elements (P, S) and the optimum soft reduction zone of continuous casting steel. Plant trials of steel SWRH82B with soft reduction were carried out to validate the theoretical model, and the results show that the solute element segregation in the centreline of the strand has been improved with the optimum soft reduction zone.

Effect of transverse distribution of secondary cooling water on corner cracks in wide thick slab continuous casting process

Abstract In the present work, a two-dimensional heat transfer model to describe the thermal behaviour of the wide thick slab during continuous casting process was developed, in which the boundary conditions for secondary cooling zone were calculated from the realistic water flux along the transverse surface of slab. The accuracy of the model calculation results were verified and calibrated by infrared thermography and nail shooting results. Furthermore, the slab temperature distribution under typical casting conditions were investigated numerically, and based on the hot ductility of microalloyed steel, the different arrangements of nozzles were optimized and designed to reduce the slab transverse corner cracks. The plant results showed that the defect rate of rolled plate corner and edge cracks were reduced from 12·6 to 3·5% with the optimised nozzles configurations.

Simulation Study of Thermal Buoyance Influence on Flow Characteristic in Single Outlet Tundish

The distribution of velocity field in single outlet tundish has been simulated through numerical solution of turbulent Navier-Stokes equation in conjunction with e − k turbulence model. The theoretical predicted results have compared with experimental ones, and excellent agreement between them has been achieved. Through comparing the computational data using coupled heat and flow method with that of using uncoupled method, it indicated that it’s necessary to utility the coupled heat and flow method in big size tundish since the thermal buoyance should not be ignored in the calculation.